The natural heart, and specifically, the cardiac muscle tissue of the natural heart (e.g., myocardium) can fail for various reasons to a point where the natural heart cannot provide sufficient circulation of blood for a body so that life can be maintained or can completely fail. Heart failure can be due to a variety of causes and/or reasons, including viral disease, idiopathic disease, valvular disease (mitral, aortic and/or both), ischemic disease, Chagas' disease and so forth. As a solution for the dysfunctional, failing and/or diseased natural heart, attempts have been made in the past to provide a treatment and/or device to assist in or entirely maintain blood circulation.
One approach to treat a failing heart has been to transplant a heart from another human or animal into a patient. The transplant procedure requires removing an existing organ (i.e., the natural heart) for substitution with another organ (i.e., another natural heart) from another human, or potentially, from an animal. Before replacing an existing organ with another, the substitute organ must be "matched " to the recipient, which can be, at best, difficult and time consuming to accomplish. Furthermore, even if the transplanted organ matches the recipient, a risk exists that the recipient's body will reject the transplanted organ and attack it as a foreign object. Moreover, the number of potential donor hearts is far less than the number of patients in need of a transplant. Although use of animal hearts would lessen the problem with fewer donors than recipients, there is an enhanced concern with rejection of the animal heart.
Another treatment and therapy for congestive heart failure has been to wrap skeletal muscle around the epicardial surface of the patient's own heart. Skeletal muscle can be an alternative to electromechanical systems (e.g., artificial hearts and/or ventricular assist devices), and thus may eliminate the need for an external power sources and/or skin penetrating power sources. In a cardiomyoplasty procedure, skeletal muscle, such as the latissimus dorsi muscle from the back, can be surgically removed from its natural anatomical position, such as across the back in the case of the latissimus dorsi muscle. Then, it is wrapped around the heart, allowed to heal, and reconditioned from a fast twitch muscle, which is susceptible to fatigue, into muscle with slow-twitch muscle fibers capable of chronic periodic contractions and that is generally fatigue resistant.
Use of a skeletal muscle wrap to power an existing natural heart has several drawbacks. Vascular interruption to the skeletal muscle while it is being removed and transplanted around the heart can lead to muscle degeneration and can adversely affect its ability to contract with sufficient force. Skeletal muscle typically requires a pre-load stretching in order to contract with sufficient force. In order to sufficiently pre-load stretch the skeletal muscle wrap, the heart has to be expanded, sometime to levels or positions that are unhealthy. This can be especially true during the end diastolic phase when the chambers of the heart are still filling with blood. Chronic overexpansion of the heart can lead to ischemic disease. Sufficient contraction of the skeletal muscle wrap does not actively occur every heart beat, and it may only occur every second or third heart beat. Moreover, a single muscle generally cannot provide sufficient contraction (e.g., pumping force) to meet cardiac stroke requirements for circulation of blood. As such, even after a skeletal wrap has been reconditioned as mentioned above, it can usually only generate enough pumping force to augment the heart's naturally occurring pumping action and thus, usually cannot replace the pumping action of the heart.
Another approach has been to either replace the existing natural heart in a patient with an artificial heart or a ventricular assist device or to affix a pump-like device in and/or around the existing natural heart. These circulatory assist devices must be powered by a source which can be external to the body. External power sources are not typically restrained by size, and sometimes can be large and/or bulky, which can decrease a patient's mobility. This can be the case even when a portable system is used for a short period of time. Some power sources, which are external to the body, power or actuate the internal device via cables, electrical cords and/or pneumatic hoses. Indefinitely having percutaneous connectors, which break through the skin, can enhance the onset of infections. A circulatory assist device can be powered by electrical power that is transmitted to the circulatory assist device using a transformer to transmit power transcutaneously through the skin. Such a power delivery system also can have drawbacks. Power to the circulatory assist device can be interrupted if the coils of the transformer become displaced from each other. Also, electrical conductors can also increase the possibility of cross coupling which can lead to power disruption because of a magnetic flux. Drawbacks on powering and delivering power to these circulatory assist devices have limited use of these devices to applications having too brief a time period to provide a real lasting benefit.
Others have suggested leaving skeletal muscle in situ and using it to power a circulatory assist device by delivering a force, due to unidirectional or linear shortening of the muscle's myofibers, by a linkage, such as a rod, cable, suture or cord having a plurality of bundled or braided fibers along its entire length. However, repeated and indefinite transmission of contractible force from muscle to an artificial device using such a linkage presents difficulties which have not been addressed. Due to repeated use, the suture would deliver significant pressure to the linkage/muscle interface, which already has a reduced blood supply. Chronic repetition of such high pressure may likely harm tissue integrity. Also, the suture would likely reposition itself closer to the distal end of the muscle since the muscle will likely remodel around the suture due to the high pressure. As such, a sufficient bond between the suture and muscle to sustain muscle contract force may not develop. This failure to establish the bond and the deteriorating condition may eventually lead to the suture becoming unattached from the muscle and failing.
As can be seen, currently available treatments, procedures, and devices for maintaining blood circulation have a number of shortcomings that contribute to the complexity of the procedure or device. The current devices and procedures are in limited supply, can be extremely invasive, and may only provide a benefit for a brief period of time. A need exists in the industry for an artificial coupling that can be used to harness the force and power of skeletal muscle in situ whereby an artificial circulation support device can be powered (e.g., pumped or otherwise actuated) repeatedly and indefinitely.